**Qadi Zada** was an Islamic mathematician who wrote a number of commentaries of works on mathematics and astronomy.

- Qadi Zada, however, is not his proper name which was Salah al-Din Musa Pasha.
- While we are commenting on his name we should also note that it is often written as Qadizada.
- It was in his home town of Bursa that Qadi Zada was brought up.
- His teacher al-Fanari realised that Qadi Zada was a young man with great abilities in mathematics and astronomy and he advised him to visit the cultural centres of the empire, Khorasan or Transoxania, where he could benefit from coming in contact with the top mathematicians of his time.
- When Qadi Zada was a young man, Timur, who is often known as Tamerlane, ruled the empire stretching across present day Iran, Iraq, and eastern Turkey.
- The cultural centres where Qadi Zada would be advised to visit would include Herat in Khorasan (today in western Afghanistan) and Bukhara and Samarkand in Transoxania.
- It was not until around 1407 that Qadi Zada set off to visit these cities.
- After visiting a number of cities, Qadi Zada reached Samarkand in about 1410.
- Ulugh Beg was only 17 years old when Qadi Zada met him at Samarkand in 1410.
- Meeting Ulugh Beg was certainly a turning point for Qadi Zada, for he would spend the rest of his life working in Samarkand.
- Qadi Zada wrote a number of commentaries on works on mathematics and astronomy during his first years in Samarkand.
- These seem to have been written for Ulugh Beg and it would appear that Qadi Zada was producing material as a teacher of the brilliant young mathematician.
- One commentary on the compendium of the astronomer al-Jaghmini was written by Qadi Zada in 1412-13, while a second commentary was on a work by al-Samarqandi.
- Qadi Zada wrote the work in 1412.
- In 1417, perhaps encouraged by Qadi Zada, Ulugh Beg began building a madrasah which is a centre for higher education.
- In addition to Qadi Zada, Ulugh Beg invited al-Kashi to join his madrasah, as well as around sixty other scientists.
- There is little doubt that al-Kashi, Qadi Zada and Ulugh Beg himself, were the leading astronomers and mathematicians at this prestigious establishment in Samarkand.
- In the letters al-Kashi praises the mathematical abilities of Ulugh Beg and Qadi Zada but considers the other scientist second rate compared with them.
- Usually these problems were too difficult for all except al-Kashi and Qadi Zada.
- Qadi Zada's most original work was a computation of sin 1° with remarkable accuracy.
- Published in 1437, in the year following Qadi Zada's death, it gives the positions of 992 stars.
- The catalogue was a collaborative effort by a number of scientists working at the Observatory but the principal contributors were certainly Ulugh Beg, al-Kashi, and Qadi Zada.
- A commentary by Qadi Zada which is incomplete, was on the astronomical treatise of Nasir ad-Din al-Tusi.
- A treatise by Qadi Zada on the problem of facing Mecca, an important problem which many Muslim astronomers and mathematicians discussed, has also survived.

Born 1364, Bursa, Turkey. Died 1436, Samarkand, Uzbekistan.

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Astronomy, Origin Turkey

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive